We can work with a lot of languages and tools in knitr, including but not limited to R, although knitr is an R package and has to be run within the R environment in the first place. Currently knitr supports Python, Ruby, Haskell, awk/gawk, sed, shell scripts, Perl, SAS, TikZ, Graphviz and C++, etc. We have to install the corresponding software package in advance to use an engine.